The present invention relates to a magnetic head read/write preamplifier within a magnetic storage system. In particular, the present invention relates to a read differential preamplifier circuit with reduced input capacitance.
A magnetic storage system includes a magnetic head which reads and writes information on a recording surface of a magnetic medium, such as a magnetic disk. The magnetic head includes an inductive coil which reads and writes the information by sensing or creating a changing magnetic field. A read/write preamplifier is connected to the coils of the magnetic head at first and second head contacts. The preamplifier includes read circuitry and write circuitry for controlling the read and write operations.
The read circuitry includes a differential amplifier with first and second inputs connected across the head contacts. During read mode operation, the magnetic head's inductive coil passes through magnetic fields caused by adjacent polarized bit positions on the recording surface. Passing the inductive coil through these magnetic fields induces a voltage differential across the first-and second read amplifier inputs. Digital information, which is stored in the selected bit positions, is read from the surface of the magnetic medium by sensing the varying polarity of the voltages induced across the first and second head contacts.
In read preamplifier design, tradeoffs must usually be made between low input voltage noise and low input capacitance. It is difficult to design the read preamplifier with both low input voltage noise and low input capacitance. Low intrinsic base resistance of the input transistor pair is desirable because as the base resistance of the input device decreases, input noise levels also decrease. Decreasing the input noise improves the signal to noise ratio of the preamplifier and results in increased sensitivity which allows the read preamplifier to read data from magnetic storage media with increased data bit densities.
In the alternative, low input capacitance is desirable because, as the input capacitance increases, the bandwidth of the read preamplifier input stage decreases. As a result, high input capacitances cause the read preamplifier to have a low bandwidth. Low bandwidth limits the maximum rate at which data may be read from the surface of the magnetic media. Currently, read preamplifier designers must choose between a high signal to noise ratio and a high read data rate.